Draft responsive three-point hitch

ABSTRACT

A three-point hitch for trailingly mounting an agricultural implement on a tractor. The hitch has three links which are connected to the tractor and are movable fore and aft. The links are interconnected at the tractor by means of a reaction linkage. The linkage is arranged to transmit only horizontal forces to a hydraulic control system for improved draft control.

[ Oct. 30, 1973 1 1 DRAFT RESPONSIVE THREE-POINT HITCH 11/1967 Schulz eta1.

[75] Inventor: Ronald D. Pitsch, Minnetonka,

Minn.

FOREIGN PATENTS OR APPLICATIONS White Farm Equipment Company, Hopkins,Minn.

Dec. 3, 1971 950,566 2/1964 Great 172/7 [73] Assignee:

[22] Filed:

Primary Examiner-Robert E. Pulfrey AttorneyDavid A. Burge 21 Appl. No.:204,729

Related U.S. Applicntion Data .8 l lc w m w n eoe mmmmu in m a d U me hch u T 0 r m mmw T mmm 1 k m TUmn R vmrhem m mm wm e. f m a a .n mnh mtC n o .lmctn 0e fa P m avma m 6.1 n m w mmmf Amwmm v WO M N U. M,

o mhn a mu f umhzb o mmmM m u is nm mmS mm smfw Ca UIF H HUN ranged totransmit only horizontal forces to a hydraulic control system forimproved draft control.

[5 6] References Cited UNITED STATES PATENTS 3,128,830 4/l964Doering..........................,.....v. 172/7 2 Claims, 3 DrawingFigures PAIENIEU E so ms 3.768568 SHEEI 1 BF 2 INVENTOR. EONALD D.0/7504 QTTOENEYE'T PMENIEDUBI 30 I975 3,768,568 SHEET 2 or 2 INVENTOR. WQONALD 0. 0/7504 4 TTOEN E Y5.

DRAFT RESPONSIVE THREE-POINT HITCH This is a cointinuation ofapplication, Ser. No. 879,213 filed Nov. 24, 1969, now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention The inventionpertains to the art of earth-working devices adapted to trail behind apropelling means such as a tractor. More particularly the inventionpertains to structures known as three-point hitches which are used tocouple implements to tractors.

2. The Prior Art The usual three-point hitch has an upper and two lowerstruts, usually referred to as links. Forward ends of the links arepivotally connected to a tractor while the rearward ends of the linksare detachably and pivotally connected to an implement. When animplement is being pulled in an earth-working operation, the lower linksare in tension and the upper link is in compression.

A mechanism is provided for raising and lowering the links to elevatethe implement to a transport position and to lower the implement to anearth-working position when desired. Typically, this elevating mechanismwill include a hydraulic system.

One objective the designer of agricultural earthworking equipment has isto provide a construction which will impose as uniform a pull or draftload as possible on a tractor as a given earth-working operation isperformed. Draft loads are horizontal forces which reflect theresistance of the earth to penetration by a plow or other earth-workingimplement. If a tractor is being used for plowing, for example, it isdesirable to adjust the depth of the plow in the earth so that the draftload imposed on the tractor is as constant as possible.

Variations in soil conditions, unevenness of the terrain andobstructions such as stones are all factors which can vary draftconditions. In known systems, attempts are made to sense thesevariations in draft conditions. With many of these systems, a sensingmechanism signals the elevating mechanism to raise or lower theimplement to compensate for the variations in draft load.

Early commercial three-point hitch arrangements equipped with draftcompensation sensed'variations in draft conditions through the upperlink. Because there are circumstances under which upper-link sensingresults in erratic control, mechanisms which sense changed draftconditions on the lower links were subsequently developed. Lower-linksensing, like upper-link sensing, has shortcomings, principal amongwhich is that forces other than draft forcesare falsely responsed to bythe draftsensing mechanism. These false responses result in improperdraft compensation.-

There have been proposals for mechanisms which sense forces of bothupper and lower linkages. One such proposal was to provide strain gaugesin the upper and lower links. While strain gauges might be effective forexperimental or test purposes, practical hardware utilizing straingauges and an electrical or electronic control of hitch elevationhas notbeen developed.

Other proposals were for a linkage interconnecting the upper and thelower links so that when draft conditions were out of balance, thelinkages would selfcompensate for draft imbalances. With these proposalsmechanical adjustments would be provided to adjust the linkage for agiven range of draft conditions. While such proposals might be used inrelatively uniform draft conditions, the mechanical adjustment requiredeven or such uniform conditions would be extremely difficult and forwidely varying draft conditions, where draft compensation is obviouslymost needed, such proposals are wholly impractical.

Still another proposal sought to sense movement of upper and lower linksoccasioned by changing draft conditions. This proposal, too, has notbeen reduced to practical hardware in that it is not capable ofaccurately summing the forces under all conditions and responding todraft forces alone.

SUMMARY OF THE INVENTION With the present invention a reaction linkageis provided. The reaction linkage includes a pair of beams which arepivotally connected to the tractor. An upper link of the hitch ispivotally connected to one beam while the lower links are connected tothe other.

A draft-sensing hydraulic system is connected to the beams. Theconnections are such that vertical forces imposed on the linkage areabsorbed by the linkage and horizontal forces are normally inequilibrium. When a change of draft forces occurs, the two beams applyhorizontal forces to the draft-sensing mechanism. These horizontalforces result in a signal being sent to the elevating mechanism whichraises or lowers the switch in response to such signal.

In the preferred arrangement, the beams are mechanically interconnected.The link-to-beam connections are relatively close to the beam-to-tractorconnections and far from the beam interconnection. This provided a greatmechanical advantage in sensing the changes in draft forces. Actual linkor beam movement in response to changing draft conditions is extremelysmall and, in fact virtually imperceptible.

Accordingly, an object of the invention is to provide a novel andimproved three-point hitch mechanism in which vertical forces areabsorbed and horizontal forces summed so that the only forcestransmitted to a connecting sensing mechanism are horizontal forces dueto changes in draft conditions.

These and other advantages will be more apparent by referring to thefollowing description and drawings wherein:

DESCRIPTION OF THE DRAWINGS FIG. 1 is a rear fragmentary, perspectiveview of a tractor showing a three-point hitch mounted thereonincorporating a reaction linkage in accordance with the invention;

FIG. 2 is a side elevational view of the hitch depicted in FIG. 1showing an implement attached thereo; and FIG. 3 is a schematic diagramshowing an analysis of forces in the hitch.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION Considering thearrangement in FIG. 1, a fragmentary rear portion of a tractor is shownat 10. A hitch 12 is mounted on the tractor 10. The hitch is adapted tobe raised and lowered by a power cylinder (not shown). A hydrauliccontrol device, for example of the type disclosed in a co-pendingapplication entitled DRAFT AND POSITION CONTROL FOR TRACTOR DRAWNIMPLEMENTS, filed July 24, 1969, and assigned to the assignee of thisapplication, automatically operates the power cylinder in accordancewith draft signals received from the hitch 12. A control rod 14transmits the signals from the hitch 12 to the hydraulic control device.The rod 14 moves longitudinally in a fore and aft manner in response tothe draft forces im posed on the hitch by an implement 16 such as a plow(FIG. 2).

While the hydraulic control device forms no part of the presentinvention, some understanding of how it functions may be helpful for abetter understanding of the invention. Controls of the type referred tomay take any one of several forms, but generally will include a valveand a valve-actuating linkage. The actuating linkage is connected tosense the draft loads on the hitch. This linkage is ordinarily connectedat the forward end to a reciprocating valve spool of the type having aplurality of lands which cover and uncover passages in the valve inaccordance with the movements of the actuating linkage. The valvedirects hydraulic fluid from a pump to the power cylinder for raisingthe hitch or exhausts fluid from the cylinder to a reservoir whenlowering the hitch.

A manual control lever accessible to the operator may be set for biasingthe valve spool in a direction to increase or decrease the draftresponsiveness. If the implement encounters soil conditions producingdraft forces in excess of the level imposed on the control by the manualdraft setting, then the valve spool becomes unbalanced causing it toshift in a direction to permit fluid supply to the power cylinder whichraises the implement relative to the tractor frame until the draftforces are reduced and equilibrium is restored. Conversely, if the draftforces are too light in relation to the draft setting for the control,then the valve spool will be shifted in the opposite direction touncover exhaust passages in the valve allowing the implement to go lowerin the soil under the force of its own weight or suction until therequired draft equilibrium is established.

As shown in FIG. 1, a powered rocker shaft extends transversely of thecenter line of the tractor and projects beyond bosses 26, 27 on theupper portion of the tractor frame. The right end portion of the rocker25 is shown broken away for clarity as viewed in FIG.

1. A pair of crank arms 28 are mounted on each endv portion of therocker but only the one in the left is shown. Each crank arm 28 projectsgenerally rearwardly of the tractor.

A pair of drop links 29 are provided. The drop links 29 are pivotallyconnected to end portions of the crank arm 28. A pair of lower struts orlinks 30 extend trailingly from the rear of the tractor. The drop links29 extend downwardly to pivotally connect onto the lower struts 30.

A rocker shaft 32 extends transversely beneath tractor axle ssembly 34.The rocker shaft 32 is freely rotatable about a horizontal axis. A crank35 is mounted on an end portion of the rocker shaft 32, at the left asviewed in FIG. 1. A beam 36 is mounted on the opposite end portion ofthe rocker shaft 32. The beam 36 forms a part of a reaction linkageassembly 40, discussed in more detail presently. The crank 35 and beam36 each project generally vertically from, and rotate in unison with,the rocker shaft 32 about its horizontal axis. Forward end portions ofthe lower links 30 are respectively connected to the crank and beam 35,

36. Since the rocker shaft 32 rotates freely, the links 30 are free tomove in a limited fore and aft manner in a direction generally parallelto the ground. The lower links 30 are disconnectably attached to theimplement 16. This attachment of the loweer links is provided by apivotal connection onto the lower portions of a rigid implement mast 41(FIG. 2).

An upper strut or link 42 is provided. The upper link 42 extends fromthe tractor above the lower links 30. The upper link 42 has its rearwardend pivotally attached to the upper portion of the implement mast 41(FIG. 2) establishing with the lower struts 30 a threepoint mountingarrangement for the implement 16. The upper link 42 is pivotallyconnected at its forward end to a beam 43. The beam 43 forms part of thereaction linkage assembly discussed presently. The pivotal connection ofthe upper link and the beam is, transversely speaking, centered on thetractor.

As shown in FIG. 2, extensions of axes of the hitch links 30 and 42intersect at a virtual center F well forward of the tractor axleassembly 34. The virtual center F is located generally on an imaginaryline known as the longitudinal axis of the tractor.

As indicated previously, the hitch 12 includes the reaction linkageassembly 40 (FIG. 1) of which the beams 36 and 43 are a part. The beam36 is rotatable about the horizontal axis of the rocker shaft 32 andprojects virtually above the axle assembly 34. The beam 43 is pivoted onan extension 45 of the boss 26 about a vertical shaft 46. The beam 43projects laterally from its pivot shaft 46 so that its outer end is injuxtaposed relationship to the upper end of the beam 36.

washer 53.

The spring is a compression spring which restrains the hitch againstrearward movement. This restraint is provided by a connection of thespring 50 to the yoke 47 by a connecting rod 55. The connecting rodpasses through spring 50 and a hole in theboss 52. One end of the rod 55carries the washer 53 and the other end is connected to the yoke 47. Astop 56 intercepts the forward movement of beam 36.

It is important to note that the outer end of the beam 43 is permittedto swing in a small arc in a horizontal plane in response to the foreand aft movements of the upper link 42. Likewise, the upper end of beam36 swings in a small arc in a vertical plane in response to the fore andaft movements of the lower links 30. The radius of each arc is equal.That is, as shown in FIG. 3, the distance between the horizontal axis ofrotation of beam 36 to its pivotalconnection with the yoke 47 (x'y) isthe same as the distance from the vertical axis of rotation of beam 43to its pivotal connection with the yoke 47 (xy).

The cooperation of beam 36, 43 on separate horizontal and verticalrotational axes is an important feature of the invention. Thisarrangement permits the use of the greatest transverse and verticallever arm lengths x, y, x, y consistent with the hitch geometry. As aresult of the very slight movement at the upper end of beam 36 and atthe outer end of beam 43' it is beneficial to the control function ifthe force transmitted is as much as possible. The extended lengths yy ofthe beams 36, 43 from the point of application of the draft force totheir ends provides a known amplification factor. Thus even slightvariations in the draft load in either the upper or lower links 30, 42will be amplified along the fore and aft line of movement of the controlrod 14. The hitch control device therefore receives a draft responsesignal reflecting a summation of forces on the upper and lower linkswhich, owing to the amplification factor, provides for more positive andaccurate control of the working depth of the implement.

With an implement in which the weight is centered to the rear of themast 41, as with the plot 16 depicted in FIG. 2, there is a considerableoverhanging load placed on the hitch l2. ln a raised or transportposition, the weight W (FIG. 3) of the implement is supported entirelyby the hitch so as to place the upper link 42 in tension T and the lowerlinks 30 in compression C. When the implement 16 is lowered intoengagement with the ground and is being pulled by the tractor, the draftloads LT act generally parallel to the lower links 30 placing them intension while the upper link 42 is normally in compression LC. Thiscondition, however, can be reversed, especially under light draftconditions, where there is a large overhanging implement mass. In thisevent, the summation of the weight reaction of the implement and thedraft loads can produce a resultant force RT acting in tension on theupper link 42 and in compression RC on the lower links 30. With priorcommercially available draft sensing devices, this set of conditionswould result in a false signal being transmitted to the automatic hitchcontrol device. With such prior devices a power cylinder would, undersuch conditions, operate in a fashion wholly inconsistent with actualdraft conditions as described earlier.

' With this invention, the possibility ofa false draft signal is largelyeliminated. False draft signals are eliminated because the reactionlinkage 40 equalizes the horizontal force components transmitted by thebeams 36, 43 from the links 30, 42. Thus the forces RT, RC imposed onthe hitch by the overhanging mass of the implement are resolved intobalanced horizontal components. This is because the links 30, 42 aremechanically interdependent in their fore and aft movements relative tothe tractor frame owing to the reaction linkage 40. Likewise thelongitudinal draft forces equal to the forces LT in the lower links 30are transmitted to the upper link 42 in the same direction andmagnitude. The transmitted force tends to equalize the forces equal toLC of compression in the link. Thus any fore or aft movements of thelower links 30 e.g., due to a change in draft loading, are followedequally by the upper link 42. It may be desirable, however, to vary theratio of the reaction linkage by changing the relationship of momentarms x, x. For example, this may be accomplished by connecting the links30 at greater distances from their horizontal axis of rotation than theupper link 42 is from its vertical axis of rotation. This imposes anover balanced condition on the linkage which avoids the problem oftenencountered in balanced servo control systems where the control isconstantly hunting equilibrium. Generally, the ratio of the distance xor x to the distance y or y will always be less than one.

From the foregoing, it will be appreciated that the invention provides adraft responsive hitch of much greater sensitivity than that afforded inthe prior art. Although only a certain specific embodiment has beendescribed, it is apparent that those skilled in the art can wellunderstand the principle of operation of the invention and possiblyenvision modifications to the specific embodiment without departing fromthe invention as defined in the appended claims.

I claim:

1. In combination with a tractor, an improved threepoint hitchcomprising:

a. upper and lower link support beams each pivotally mounted on thetractor and oriented generally perpendicular to one another;

b. an upper draft link pivotally connected to said upper beam and a pairof lower draft links pivotally connected to said lower beam;

0. connection means interconnecting said beams such that a tensionloading applied through the connections of said lower draft links willurge said interconnected beams in a direction opposite to that urged bya compression loading applied through the connection of said upper draftlink;

d. said interconnection between said beams being spaced from saidpivotal mountings of each of said beams;

e. said upper draftlink pivotal connection being located intermediatethe pivotal mounting of said upper beam and said interconnection betweensaid beams;

f. said lower draft link pivotal connections being located along an axisintersecting said lower beam at a location intermediate the pivotalmounting of said lower beam and said interconnection between said beams;

g. draft-sensing means connected to said beams to sense concurrentmovement of said beams due to variations of draft force applied when inuse by a connected draft load producing implement through said draftlinks;

h. said draft-sensing means being connected to said beams at a locationfurther from each of said beam mountings than are said pivotal linkconnections from said beam mountings, whereby a second class leverarrangement is provided which increases the sensitivity of saiddraft-sensing means by causing said draft-sensing means to move througha greater distance in response to a change of draft forces due to saiddraft links, and the movement of said draftsensing means is duesubstantially only to variations in draft forces;

. draft control means connected with atleast one of said draft links andoperatively connected to said draft-sensing means to adjust the positionof said draft links according to draft variations sensed by said sensingmeans;

j. said pivotal connection of said upper beam to the tractor mounts saidupper beam for pivotal movement about a generally vertical axis;

k. said pivotal connection of said lower beam to the tractor mounts saidlower beam for pivotal movevment about a generally horizontal axis; and,

1. said interconnection between said beams being located above saidpivotal connection of said lower beam and laterally of said pivotalconnection of said upper beam.

c. whereby a compression force carried by said upper link will becounteracted by a tension force carried by said lower links such that ifsaid forces are of substantially equal magnitude, they will causesubstantially no resultant movement of said interconnected beams.

PatentvNo. 3'768-563 Dated October 30, 1973 RONALD D. PI'ISCHInventor(s) It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 28, delete "switch" and substitute hitch Column 5, line2, following is insert amplified Column 1, line 2, "cointinuation",should read continuation Signed and sealed this 7th day of May 197i;-

(SEAL) Attest:

EDWARD M.FIETCHEB., JR. C. l IARSHALL DAMN Attesting OfficerCommissioner of Patents F ORM PO-105O (10-69) USCOMM-DC 60376-P59 U.S.GOVERNMENT PRINTING OFFICE: 1969 0-366-334

1. In combination with a tractor, an improved three-point hitchcomprising: a. upper and lower link support beams each pivotally mountedon the tractor and oriented generally perpendicular to one another; b.an upper draft link pivotally connected to said upper beam and a pair oflower draft links pivotally connected to said lower beam; c. connectionmeans interconnecting said beams such that a tension loading appliedthrough the connections of said lower draft links will urge saidinterconnected beams in a direction opposite to that urged by acompression loading applied through the connection of said upper draftlink; d. said interconnection between said beams being spaced from saidpivotal mountings of each of said beams; e. said upper draft linkpivotal connection being located intermediate the pivotal mounting ofsaid upper beam and said interconnection between said beams; f. saidlower draft link pivotal connections being located along an axisintersecting said lower beam at a location intermediate the pivotalmounting of said lower beam and said interconnection between said beams;g. draft-sensing means connected to said beams to sense concurrentmovement of said beams due to variations of draft force applied when inuse by a connected draft load producing implement through said draftlinks; h. said draft-sensing means being connected to said beams at alocation further from each of said beam mountings than are said pivotallink connections from said beam mountings, whereby a second class leverarrangement is provided which increases the sensitivity of saiddraft-sensing means by causing said draftsensing means to move through agreater distance in response to a change of draft forces than do saiddraft links, and the movement of said draft-sensing means is duesubstantially only to variations in draft forces; i. draft control meansconnected with at least one of said draft links and operativelyconnected to said draft-sensing means to adjust the position of saiddraft links according to draft variations sensed by said sensing means;j. said pivotal connection of said upper beam to the tractor mounts saidupper beam for pivotal movement about a generally vertical axis; k. saidpivotal connection of said lower beam to the tractor mounts said lowerbeam for pivotal movement about a generally horizontal axis; and, l.said interconnection between said beams being located above said pivotalconnection of said lower beam and laterally of said pivotal connectionof said upper beam.
 2. The combination of claim 1 wherein: a. thespacings between said pivotal mountings and said interconnection foreach of said beams are substantially equal; and, b. the distancesbetween said pivotal mountings and said pivotal connections for each ofsaid beams are substantially equal; c. whereby a compression forcecarried by said upper link will be counteracted by a tension forcecarried by said lower links such that if said forces are ofsubstantially equal magnitude, they will cause substantially noresultant movement of said interconnected beams.